Progressive split injection strategies to combustion and emissions improvement of a heavy-duty diesel engine with ammonia enrichment

The global greenhouse effect has intensified, and adopting carbon-free fuels in internal combustion engines to replace traditional fossil energy has become a key strategy for energy conservation and emission reduction. To optimize the combustion efficiency and stability of the ammonia-diesel dual-fuel engine, this study proposes a diesel main pulse split injection strategy. The effects of key parameters in the split injection strategy on the combustion characteristics and emission performance of the engine were systematically analyzed using computational fluid dynamics simulation methods. The results reveal that the optimized split injection strategy can effectively promote the uniform distribution of the mixture under the ammonia-diesel dual-fuel mode, thus achieving a more thorough and rapid combustion process. At the ammonia energy fraction of 40 %, better performance can be obtained. Appropriately increasing the proportion of diesel fuel in the first pulse of injection significantly facilitates the combustion process, accelerates the ammonia flame propagation, and reduces the problem of high unburned ammonia emissions compared to the single injection strategy. In addition, by adjusting the dwell between the two pulses, an optimal dwell between the two pulses can be obtained, promoting the diesel injected in the second pulse to accelerate the combustion process of the residual ammonia in the combustion chamber. An in-depth study of the second injection pulse width shows that a narrower secondary injection pulse width is beneficial to the optimization of engine performance. Quantitative analysis indicates that the scheme applying 40 % ammonia energy fraction and combining it with the optimized split injection strategy provides a certain increase in the efficiency of the engine. Furthermore, the study discovered that under the ammonia-diesel dual-fuel mode, unburned ammonia and HC emissions can be reduced to near-zero levels. Compared to the single injection of diesel, this strategy reduces by 30.9 % in NOx and 36.2 % in greenhouse gas emissions.